1. Field of the Invention
This invention relates to an illuminating apparatus and a projecting apparatus, and particularly is preferable for a liquid crystal projector for projecting the enlarged image of a liquid crystal display element (liquid crystal panel) onto a screen or a wall by a projection lens.
2. Related Background Art
There have heretofore been proposed various liquid crystal projectors for illuminating a liquid crystal panel by a light beam from a light source, and enlarging and projecting an image based on transmitted light or reflected light from a liquid crystal panel onto a screen or a wall by a projection lens.
A liquid crystal panel of the TN type which can relatively easily obtain an image of high contrast utilizes the polarizing characteristic of liquid crystal. Therefore, usually a polarizer and an analyzer are provided before and behind the liquid crystal panel. Such polarizing filters have a characteristic of transmitting therethrough polarized light of light incident thereon in a particular direction of polarization and intercepting polarized light in a direction of polarization orthogonal to said direction of polarization. Thus, at least a half of light from the light source of the liquid crystal projector is intercepted by the polarizer, and the brightness of an projected image has been not sufficient.
FIG. 1 of the accompanying drawings is a schematic view of the essential portions of a projector proposed in Japanese Laid-Open Patent Application No. 61-90584 which has solved this problem of brightness.
In the liquid crystal projector of FIG. 1, a light beam from a light source 201 is made to enter a polarized light separating element 202 for separating random polarized light into two polarized components (P-polarized light and S-polarized light) orthogonal to each other through an infrared cut filter 208 and a lens 207. A half wavelength plate 203 is provided in the optical path of the S-polarized light which is reflected light of a light be passed through the polarized light separating element 202. The direction of polarization of the polarized light transmitted through the half wavelength plate is rotated by 90.degree. by the half wavelength plate and this light is caused to emerge in the same way as the P-polarized light which is the transmitted light. The optical paths of two polarized lights from the polarized light separating element 202 are bent and superposed one upon the other on a liquid crystal panel 205 by the use of a mirror 209 and a prism 204 so that all of the light from the light source 201 can be utilized.
In the liquid crystal projector shown in FIG. 1, the polarized light separating element 202 requires the same degree of size as that of the lens 207 or a reflector 206, and this leads to the disadvantage that the projector becomes bulky and expensive and further, since the light beam is separated into two beams, the illuminating light beam becomes about twice as large as that in the prior art, and to enable all of the illuminating light beam to be transmitted through a projection lens, the opening diameter (F.sub.NO) of the projection lens becomes two or more times that in the prior art, and this also has led to a disadvantage in designing.
In contrast, in an illuminating apparatus for the liquid crystal projector of Japanese Laid-Open Patent Application No. 8-304739, a polarization separating element, a beading mirror and a half wavelength plate are each made into an array to thereby achieve the thinning of a polarization converting portion and moreover, the size of the illuminating light beam is maintained at the same degree as that in the prior art so that a conventional projection lens can be used.